Hitherto, there is known a vehicle seat which includes a seat back, and in which a seat back frame for the seat back is provided with an airbag module at a side thereof, a pair of stay cloths are provided at inner sides of front and side cover portions of a trim cover for the seat back, one terminals of the stay cloths are sewn together with terminals of the front and side cover portion of the trim cover so as to form a breakage portion of the trim cover for allowing expansion of an air bag, and the other terminals of the stay cloths are fixed to the seat back frame, whereby the air bag module is enclosed by the stay cloths (Japanese Patent Application Laid-Open No. Hei. 11-78762).
In the conventional seat back, the seat back frame is formed into a substantially quadrilateral shape by bending a metal pipe, and the other terminals of the stay cloths are fixed to a retainer or a zigzag spring provided at the seat back frame whereby the airbag module is enclosed by the stay cloths.
Also, there is known a seat back frame which is formed into a substantially quadrilateral shape, made of a light alloy such as a magnesium alloy, an aluminum alloy or the like, and comprises an upper section, left and right sections, and a lower section (Japanese Patent Application Laid-Open No. 2001-114004). When an airbag module is mounted to this seat back frame, it is conceivable that a retainer member for retaining terminals of stay cloths is provided at the seat back frame.
The retainer member can be secured to the seat back frame made of a light alloy, using bolts and nuts. However, in a case where the retainer member is fixed to the light alloy seat back frame by causing the bolts to be penetrated the seat back frame and holding the bolts in their places with the nuts, heads of the bolts or the nuts are bitten into regions of the light alloy seat back frame. As a result, the regions of the seat back frame are decreased in thickness, so that rigidity of the seat back frame is reduced.